Attention has currently been drawn to an organic light-emitting element as a thin-type light-emitting member. An organic light-emitting element can provide a high luminance using low power and is excellent in terms of visibility, a response speed, a service life, and power consumption. The light use efficiency thereof, however, is on the order of 20%, and hence there is a large loss in an organic light-emitting element.
FIG. 9 is a schematic sectional view of a conventional organic light-emitting element. An organic light-emitting element 100 is formed by stacking, in order from a lower layer in the figure, a metal electrode 101, an organic light-emitting layer 102, a transparent electrode 103, and a transparent substrate 104. In the figure, arrows 110a to 110e represent characteristic ones of light rays generated from the organic light-emitting layer 102.
The light ray 110a is a light ray in a perpendicular direction to the organic light-emitting layer 102 that is a light-emitting plane, which is transmitted through the transparent substrate 104 to be extracted to a light extraction side (air side). The light ray 110b is a light ray that has entered an interface between the transparent substrate 104 and the air at a shallow angle not more than a critical angle and is refracted at the interface between the transparent substrate 104 and the air to be extracted to the light extraction side. The light ray 110c is a light ray that has entered the interface between the transparent substrate 104 and the air at an angle deeper than the critical angle and is totally reflected off the interface between the transparent substrate 104 and the air, thus failing to be extracted to the light extraction side. A loss attributable to this is referred to as a substrate loss, and due thereto, there is typically a loss on the order of 20%.
The light ray 110d is a light ray satisfying a resonance condition among light rays that have entered an interface between the transparent electrode 103 and the transparent substrate 104 at an angle deeper than a critical angle. The light ray 110d is totally reflected off the interface between the transparent electrode 103 and the transparent substrate 104, which establishes a waveguide mode in which the light ray 110d is trapped inside the organic light-emitting layer 102 and the transparent electrode 103. A loss attributable to this is referred to as a waveguide loss, and due thereto, there is typically a loss on the order of 20 to 25%. The light ray 110e is a light ray that enters the metal electrode 101 to interact with a free electron in the metal electrode 101, which establishes a plasmon mode that is one form of the waveguide mode, in which the light ray 110e is trapped in the vicinity of a surface of the metal electrode 101. A loss attributable to this is referred to as a plasmon loss, and due thereto, there is typically a loss on the order of 30 to 40%.
As described above, in the conventional organic light-emitting element 100, there are a substrate loss, a waveguide loss, and a plasmon loss, and hence it has been sought to reduce these losses so as to extract a maximum possible amount of light.
For example, Patent Document 1 discloses an organic EL (electro luminescence) device in which a light scattering portion constituted by a lens sheet is provided on a light extraction surface side. Furthermore, Patent Document 2 discloses a substrate for a light-emitting device and a light-emitting device. The substrate for a light-emitting device disclosed therein is composed of a high refractive index convexo-concave layer having a refractive index of not less than 1.6 and an average surface roughness of not less than 10 nm, which is provided on a surface of the substrate at least on one side thereof, and one or more base material layers each having a refractive index of not less than 1.55, and is used on a light-emitting surface side of the light-emitting device.